Input's ascii reader is now more resilient.

By default, the ASCII reader does not fail on errors anymore.
If there is a problem parsing a line, a reporter warning is
written and parsing continues.  If the file is missing or can't
be read, the input thread just tries again on the next heartbeat.

Options have been added to recreate the previous behavior...

const InputAscii::fail_on_invalid_lines: bool;
and
const InputAscii::fail_on_file_problem: bool;

They are both set to `F` by default which makes the input readers
resilient to failure.

testing/btest/scripts/base/frameworks/input/missing-file-initially.bro

@@ -0,0 +1,47 @@
+# This tests files that don't exist initially and then do later during
+# runtime to make sure the ascii reader is resilient to files missing.
+# It does a second test at the same time which configures the old 
+# failing behavior.
+
+# @TEST-EXEC: btest-bg-run bro bro %INPUT
+# @TEST-EXEC: btest-bg-wait -k 5
+# @TEST-EXEC: btest-diff bro/.stdout
+# @TEST-EXEC: btest-diff bro/.stderr
+
+@TEST-START-FILE does-exist.dat
+#separator \x09
+#fields	line
+#types	string
+now it does
+and more!
+@TEST-END-FILE
+
+redef exit_only_after_terminate = T;
+
+@load base/frameworks/input
+
+module A;
+
+type Val: record {
+	line: string;
+};
+
+event line(description: Input::EventDescription, tpe: Input::Event, v: Val)
+	{
+	print v$line;
+	}
+
+event line2(description: Input::EventDescription, tpe: Input::Event, v: Val)
+	{
+	print "DONT PRINT THIS LINE";
+	}
+
+
+event bro_init()
+	{
+	Input::add_event([$source="../does-not-exist.dat", $name="input", $reader=Input::READER_ASCII, $mode=Input::REREAD, $fields=Val, $ev=line, $want_record=T]);
+	Input::add_event([$source="../does-not-exist.dat", $name="input2", $reader=Input::READER_ASCII, $mode=Input::REREAD, $fields=Val, $ev=line2, $want_record=T, 
+	                  $config=table(["fail_on_file_problem"] = "T")]);
+
+	system("sleep 2; mv ../does-exist.dat ../does-not-exist.dat;");
+	}